1. Field of the Invention
The present invention relates, generally, to mechanisms for controlling machines, and more particularly to a cam mechanism for controlling a packaging machine.
2. Background Information
Machines that perform repetitive tasks are often controlled by at least one mechanical cam and follower mechanism. Each axis of motion may have a separate cam and follower mechanism. The follower is connected to a mechanical linkage which is connected to some mechanism or device that performs the desired function. As the cam rotates, the follower moves over a contoured surface or edge of the cam. As the follower moves, it drives the linkage and the connected mechanism or device through a specific pattern of motion to accomplish the desired function. Motions of multiple mechanisms are synchronized by synchronizing the relative motion of multiple cams by mechanical drive means.
Any particular machine may be able to produce a variety of related products by changing the set-up of the machine. Such a set up change requires changing the cam(s). This means disconnecting the follower mechanism from the cam, physically removing the cam (which may be a rather large heavy metal plate), installing the new cam, and reconnecting the follower mechanism. Cams are usually located inside a machine and they may be difficult to access, which further complicates changing the cam.
Alternatives to mechanical cams include optical cams and computer control. Optical cams have an optical sensor which tracks a line of sharp contrast on a rotating drum. The position of the optical sensor is related to the physical position of a mechanism on the machine being controlled by the cam. The line of sharp contrast is typically formed by a contoured sheet of black mylar or other similar material attached to a white drum. While a variety of mylar cams are easier to handle and store than metal cams, each change of product still requires changing the mylar cam.
Computer control uses numeric data to control drive motors which in turn control the mechanisms in the machine. The "flight path" of each axis of motion must be programmed, and the relative motion of all axes synchronized, typically by time or by position of one axis. While programming the machine for the first product may be complicated, subsequent variations may be more easily programmed by changing a few parameters. Many programs are easily stored in the computer memory or on a computer disk. Changing the set-up simply requires reloading the program into the computer that controls the machine.
Computer control offers the most flexibility, but is also the most expensive. It is very useful where a machine must be able to perform a large variety of very complicated operations, such as on a milling machine for making three-dimensional shapes. Optical cam control may be less expensive but is less flexible than computer control. It is useful where a machine may perform many variations of the same basic movement such as on a filament winding machine that winds fiberglass filaments onto a variety of mandrels in a variety of patterns.
For machines that perform a simple repetitive operation with only a few variations, mechanical control using mechanical cams is still a very efficient and cost effective. It would, however, be more efficient and cost effective if one cam could be used on more than one product or operation without having to completely remove and change the cam. Applicant's invention provides a mechanical cam which can be used for two related operations by loosening and rotating the cam approximately 170 degrees and retightening it rather than removing it and replacing it.